Doctors say the government's decision to ration Viagra is arbitrary, "bizarre" and unfair.

Health Secretary Frank Dobson has set out guidelines which limit the prescription of Viagra on the NHS to people with certain physical problems and severe psychological distress.

Dr John Dean, a GP specialising in erectile dysfunction, said: "This is arbitrary and does not go anywhere to meeting clinical need for the majority of impotent men."

He said only about 20-25% of patients he saw with impotence were covered by Mr Dobson's categories.

If coronary artery disease, including high blood pressure, was included, this would lift the number to 80%.

Fifty per cent of diabetics become impotent as a result of their illness compared with 40% of people with coronary artery disease.

"They are just as likely to suffer and they did not choose their problem," he said.

Psychological causes

He added that it was very difficult to draw a line between physical and psychological causes of impotence in many cases.

A quarter of cases of diabetic impotence were caused by psychological rather than physical reasons, he said.

"There is not a guaranteed diagnostic test which can show whether impotence is due to physical or psychological factors," he said.

Moreover, Viagra did not work as well for diabetics as for people with coronary artery disease.

Only 55-60% of diabetics responded to Viagra, he claimed. Men with coronary heart disease were more likely to respond and the drug was effective for 80% of men with psychological problems.

"He has chosen a group which is likely to respond the least well to the drug," said Dr Dean.

He believes the decision to leave out some physical causes of impotence is due to cost.

More people have coronary artery disease than diabetes and it was more difficult to diagnose borderline vascular disease than diabetes.

More expensive treatments

Doctors also believe it is illogical to restrict Viagra while still allowing more expensive treatments for impotence which are less safe and more expensive, for example, injection therapy.

Dr Angela Coulter: the NHS has to set priorities

And they predict that hospital specialists will be inundated with patients who say their impotence is due to severe psychological problems.

Dr Dean said GPs were better equipped to decide if a person's impotence was due to psychological problems as they knew the person's history and personal circumstances.

He said specialists in urological problems would not necessarily be skilled in psychology.

Dr John Chisholm of the British Medical Association has also hit out at the "unjustifiable" restrictions on Viagra prescription.

The BMA's meeting on the subject on Thursday morning forced the government's hand after months of delay.

But NHS managers have backed the decision. Stephen Thornton, chief executive of the NHS Confederation, said: "Setting limits to healthcare is never easy. The government has been very brave with these proposals."

Dr Angela Coulter, director of policy and development for the King's Fund charity, also welcomed "clear rules" on Viagra.

She said: "There does have to be some control. The NHS has to set priorities. It cannot afford to provide everything people might want."

She added that previously doctors and health authorities had had to decide where to draw the line, but said the government had now recognised that this could not go on.

The government is setting up the National Institute for Clinical Excellence later this year which will decide on similar cases in the future.

Patients group backs Dobson

Roger Goss, of the Patients' Association, said Mr Dobson's stance was "eminently responsible and sensible".

Roger Goss backed the government

He said: "Doctors are going to be able to treat people who have deep emotional problems which if they did not get treatment might cause them even more trouble and make them a bigger cost to the health service.

"But for people like me, 50-year-olds who might see this as an opportunity to have a bit more fun in life, it is not realistic to allow me to subsidised."

Mr Goss said the Patients' Association wanted the government to consult the public on what the priorities for the health service should be.

However, a spokeswoman for the Impotence Association said it was "extremely disappointed" by Mr Dobson's announcement.

She stated: "These are extremely restrictive guidelines.

"They don't take into account people suffering impotence from the side effects of medicines or high blood pressure and they make up a huge majority of impotence sufferers."